Question: Carlos has $\dfrac45$ of a tank of fuel in his car. He uses $\dfrac{1}{10}$ of a tank per day. How many days will his fuel last?
Solution: We can think about this problem like this: $ {\text{number of days}} = {\text{all the fuel}} \div {\text{amount used per day}}$ ${\text{?}} = {\dfrac45 \text{tank}} \div {\dfrac{1}{10} \text{tank}}$ $\phantom{?} = {\dfrac45} \times \dfrac{10}{1} ~~~~~~~{\text{Rewrite dividing by} {\dfrac{1}{10}} \text{ as multiplying by} \dfrac{10}{1}}$ $\phantom{?} =\dfrac{4 \times 10}{5 \times 1}$ $\phantom{?} =\dfrac{40}{5}$ $\phantom{?} = {8 \text{ days}}$ His fuel will last $8$ days.